Scientists have uncovered ancient plague DNA in 4,000-year-old sheep remains, providing new insights into the spread of diseases between animals and humans across Eurasia during the Bronze Age.
Long before the infamous Black Death ravaged Europe in the Middle Ages, an earlier strain of plague circulated widely across Eurasia. For years, researchers struggled to understand how this ancient disease managed to spread so extensively during the Bronze Age, which spanned from approximately 3300 to 1200 B.C., and persisted for nearly two millennia. Unlike later plagues that were transmitted by fleas, this earlier version posed a unique challenge for scientists seeking to unravel its mysteries.
Recent findings have shed light on this enigma, revealing a surprising clue: the remains of a domesticated sheep that lived over 4,000 years ago. Researchers discovered DNA from the plague bacterium Yersinia pestis in the tooth of this Bronze Age sheep, unearthed in what is now southern Russia. This groundbreaking discovery, detailed in a study published in the journal Cell, marks the first known evidence of the ancient plague infecting animals, not just humans, and provides crucial insights into how the disease may have spread.
“It was alarm bells for my team,” said Taylor Hermes, a University of Arkansas archaeologist and co-author of the study. “This was the first time we had recovered the genome from Yersinia pestis in a non-human sample.”
The discovery was serendipitous, as researchers faced significant challenges when testing livestock DNA in ancient samples. “When we test livestock DNA, we get a complex genetic soup of contamination,” Hermes explained. “This is a large barrier, but it also gives us an opportunity to look for pathogens that infected herds and their handlers.”
The meticulous and time-consuming process involved separating tiny, damaged fragments of ancient DNA from contamination introduced by soil, microbes, and even modern humans. The DNA recovered from ancient animals is often fragmented into pieces as small as 50 “letters,” in stark contrast to a complete human DNA strand, which contains over 3 billion letters. Additionally, animal remains are typically more challenging to study due to their often poor preservation compared to human remains, which were frequently buried with care.
This finding enhances our understanding of how the plague likely spread through close interactions among people, livestock, and wild animals as Bronze Age societies expanded their herds and traveled further with horses. The Bronze Age was characterized by the widespread use of bronze tools, large-scale animal herding, and increased travel—conditions that may have facilitated the movement of diseases between animals and humans.
When the plague re-emerged in the 1300s during the Black Death, it decimated an estimated one-third of Europe’s population. “It had to be more than people moving,” Hermes noted. “Our plague sheep gave us a breakthrough. We now see it as a dynamic between people, livestock, and some still unidentified ‘natural reservoir’ for it.”
Researchers believe that sheep likely contracted the bacteria from another animal, such as rodents or migratory birds, which carried the pathogen without exhibiting symptoms and subsequently transmitted it to humans. This finding underscores the ongoing risk of zoonotic diseases—those that jump from animals to humans—especially as human populations encroach on new environments and interact more closely with wildlife and livestock.
“It’s important to have a greater respect for the forces of nature,” Hermes emphasized.
While this study is based on a single ancient sheep genome, which limits the conclusions that can be drawn, researchers acknowledge the need for more samples to fully comprehend the spread of the plague. They plan to investigate additional ancient human and animal remains from the region to ascertain the extent of the plague’s reach and identify which species may have contributed to its transmission.
Furthermore, the researchers aim to pinpoint the wild animal that originally carried the bacteria and gain a deeper understanding of how human movement and livestock herding facilitated the disease’s spread across vast distances. Insights from this research could prove invaluable in anticipating the emergence of animal-borne diseases in the future.
The study was led by scientists at the Max Planck Institute for Infection Biology, with senior authors Felix M. Key of the Max Planck Institute for Infection Biology and Christina Warinner of Harvard University and the Max Planck Institute for Geoanthropology. The research received support from the Max Planck Society, which has also funded subsequent work in the region.
According to Fox News, the implications of these findings extend beyond historical curiosity, highlighting the intricate relationships between humans, animals, and the pathogens that can emerge from these interactions.